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United States Patent |
6,252,005
|
Niyogi
|
June 26, 2001
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Thermal oxidative stability of acrylic polymers
Abstract
The thermal oxidative stability of acrylic grafted polymers is improved by
(a) graft polymerizing monomers selected from the group consisting of (i)
an ester or salt of an unsubstituted or 1-3 C alkyl-substituted acrylic
acid and (ii) an ester or salt of an unsubstituted or 1-3 C
alkyl-substituted acrylic acid and about 1 to about 10 mole %, based on
the total monomers added, of an unsubstituted or 1-3 C alkyl-substituted
acrylic acid, to a backbone of a propylene polymer material in the
presence of a 4-vinyl-substituted 5-12 C cyclic 1-alkene, wherein the
total amount of polymerized monomer is about 20 to about 200 parts per
hundred parts of the propylene polymer material and the vinyl-substituted
cyclic alkene is present in an amount of about 1 mole % to about 30 mole
%, based on the total moles of monomer added, and (b) removing any
unreacted grafting monomer from the resulting grafted propylene polymer
material, decomposing any unreacted initiator, and deactivating any
residual free radicals in the material, wherein steps (a) and (b) are
carried out in a substantially non-oxidizing environment.
Inventors:
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Niyogi; Suhas G. (Bear, DE)
|
Assignee:
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Montell Technology Company BV (NL)
|
Appl. No.:
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130976 |
Filed:
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August 7, 1998 |
Current U.S. Class: |
525/297; 525/301; 525/309; 525/313 |
Intern'l Class: |
C08F 289/00 |
Field of Search: |
525/297,301,309,313
|
References Cited
U.S. Patent Documents
4490507 | Dec., 1984 | Abe et al. | 525/263.
|
4599384 | Jul., 1986 | Farona et al. | 525/245.
|
4904404 | Feb., 1990 | Liu et al. | 252/51.
|
5140074 | Aug., 1992 | DeNicola et al. | 525/263.
|
5411994 | May., 1995 | Galli et al. | 521/50.
|
5852124 | Dec., 1998 | Wang et al. | 525/316.
|
Foreign Patent Documents |
229 139 | Nov., 1984 | DD.
| |
239685 | Oct., 1987 | EP.
| |
420615 | Apr., 1991 | EP.
| |
522233 | Jan., 1993 | EP.
| |
849318 | Jun., 1998 | EP.
| |
899277 | Mar., 1999 | EP.
| |
98/17701 | Apr., 1998 | WO.
| |
Other References
Glazkov, CAPLUS AN 1999:755859, 1999.*
Glazkov et al. , Proizvod. Ispol'z. Elastomerov (5), p. 6-9, 1997.*
M. Ratzsch et al., "Challenges in Polypropylene by Chemical Modification",
Macromol. Symp., 129, p. 55-77, 1998.
|
Primary Examiner: Mullis; Jeffrey
Claims
I claim:
1. A graft copolymer comprising a backbone of a propylene polymer material
to which is graft polymerized chains of monomers selected from the group
consisting of (i) an ester or salt of an unsubstituted acrylic acid or an
acrylic acid substituted at the .alpha.-carbon atom by a 1-3 C alkyl group
and (ii) an ester or salt of an unsubstituted acrylic acid or an acrylic
acid substituted at the a-carbon atom by a 1-3 C alkyl group and about 1
to about 10 mole %, based on the total monomers added, of an unsubstituted
acrylic acid or an acrylic acid substituted at the .alpha.-carbon atom by
a 1-3 C alkyl group, having 4-ethylidene-substituted 5-12 C cyclic
1-alkene groups derived from a 4-vinyl-substituted 5-12 C cyclic 1-alkene
at the chain ends.
2. The graft copolymer of claim 1 wherein the propylene polymer material is
selected from the group consisting of
(a) a homopolymer of propylene having an isotactic index greater than 80;
(b) a copolymer of propylene and an olefin selected from the group
consisting of ethylene and 4-10 C alpha-olefins, provided that when the
olefin is ethylene, the maximum polymerized ethylene content is 10% by
weight and when the olefin is a 4-10 C alpha-olefin, the maximum
polymerized content thereof is 20% by weight, the copolymer having an
isotactic index greater than 85;
(c) a terpolymer of propylene and two olefins selected from the group
consisting of ethylene and 4-8 C alpha-olefins, provided that the maximum
polymerized 4-8 C alpha-olefin content is 20% by weight, and, when
ethylene is one of the olefins, the maximum polymerized ethylene content
is 5% by weight, the terpolymer having an isotactic index greater than 85;
(d) an olefin polymer composition comprising:
(i) about 10% to about 60% by weight of a propylene homopolymer having an
isotactic index greater than 80, or a copolymer selected from the group
consisting of a copolymer of (a) propylene and ethylene, (b) propylene,
ethylene and a 4-8 C alpha-olefin, and (c) propylene and a 4-8 C
alpha-olefin, the copolymer having a polymerized propylene content of more
than 85% by weight and an isotactic index greater than 85;
(ii) about 5% to about 25% of a copolymer of ethylene and propylene or a
4-8 C alpha-olefin that is insoluble in xylene at ambient temperature, and
(iii) about 30% to about 70% of an elastomeric copolymer selected from the
group consisting of a copolymer of (a) ethylene and propylene, (b)
ethylene, propylene, and a 4-8 C alpha-olefin, and (c) ethylene and a 4-8
C alpha-olefin, the copolymer optionally containing about 0.5% to about
10% of a polymerized diene, and containing less than 70% by weight of
polymerized ethylene and being soluble in xylene at ambient temperature,
and having an intrinsic viscosity of about 1.5 to about 4.0 dl/g,
wherein the total amount of (ii) and (iii), based on the total olefin
polymer composition, is about 50% to about 90%, the weight ratio of
(ii)/(iii) is less than 0.4, and the composition is prepared by
polymerization in at least two stages, and has a flexural modulus of less
than 150 MPa; or
(e) a thermoplastic olefin comprising:
(i) about 10% to about 60% of a propylene homopolymer having an isotactic
index greater than 80, or a copolymer selected from the group consisting
of a copolymer of (a) ethylene and propylene, (b) ethylene, propylene, and
a 4-8 C alpha-olefin, and (c) ethylene and a 4-8 C alpha-olefin, the
copolymer having a polymerized propylene content greater than 85% and an
isotactic index of greater than 85;
(ii) about 20% to about 60% of an amorphous copolymer selected from the
group consisting of a copolymer of (a) ethylene and propylene, (b)
ethylene, propylene, and a 4-8 C alpha-olefin, and (c) ethylene and a 4-8
C alpha-olefin, the copolymer optionally containing about 0.5% to about
10% of a polymerized diene and containing less than 70% polymerized
ethylene and being soluble in xylene at ambient temperature; and
(iii) about 3% to about 40% of a copolymer of ethylene and propylene or a
4-8 C alpha-olefin that is insoluble in xylene at ambient temperature,
wherein the thermoplastic olefin has a flexural modulus of greater than
150 but less than 1200 MPa.
3. The graft copolymer of claim 2 wherein the propylene polymer material is
a propylene homopolymer.
4. The graft copolymer of claim 1 wherein an ester of an acrylic acid
substituted at the .alpha.-carbon atom by a 1-3 C alkyl group is graft
polymerized.
5. The graft copolymer of claim 4 wherein the ester is methyl methacrylate.
6. The graft copolymer of claim 1 wherein the 4-vinyl-substituted cyclic
1-alkene is 4-vinyl-1-cyclohexene.
7. The graft copolymer of claim 5 wherein the 4-vinyl substituted cyclic
1-alkene is 4-vinyl-1-cyclohexene.
8. A method for improving the thermal oxidative stability of acrylic
grafted polymers comprising:
(a) graft polymerizing monomers selected from the group consisting of (i)
an ester or salt of an unsubstituted acrylic acid or an acrylic acid
substituted at the .alpha.-carbon atom by a 1-3 C alkyl group and (ii) an
ester or salt of an unsubstituted acrylic acid or an acrylic acid
substituted at the .alpha.-carbon atom by a 1-3 C alkyl group and about 1
to about 10 mole %, based on the total monomers added, of an unsubstituted
acrylic acid or an acrylic acid substituted at the a-carbon atom by a 1-3
C alkyl group, to a backbone of a propylene polymer material in the
presence of a 4-vinyl-substituted 5-12 C cyclic 1-alkene, wherein the
total amount of polymerized monomers is about 20 to about 200 parts per
hundred parts of the propylene polymer material and the
4-vinyl-substituted cyclic 1-alkene is present in an amount of about 1
mole % to about 30 mole %, based on the total moles of monomers added, and
(b) removing any unreacted grafting monomer from the resulting grafted
propylene polymer material, decomposing any unreacted initiator, and
deactivating any residual free radicals in the material, wherein steps (a)
and (b) are carried out in a substantially non-oxidizing environment.
9. The method of claim 8 wherein the propylene polymer material is selected
from the group consisting of
(a) a homopolymer of propylene having an isotactic index greater than 80;
(b) a copolymer of propylene and an olefin selected from the group
consisting of ethylene and 4-10 C alpha-olefins, provided that when the
olefin is ethylene, the maximum polymerized ethylene content is 10% by
weight and when the olefin is a 4-10 C alpha-olefin, the maximum
polymerized content thereof is 20% by weight, the copolymer having an
isotactic index greater than 85;
(c) a terpolymer of propylene and two olefins selected from the group
consisting of ethylene and 4-8 C alpha-olefins, provided that the maximum
polymerized 4-8 C alpha-olefin content is 20% by weight, and, when
ethylene is one of the olefins, the maximum polymerized ethylene content
is 5% by weight, the terpolymer having an isotactic index greater than 85;
(d) an olefin polymer composition comprising:
(i) about 10% to about 60% by weight of a propylene homopolymer having an
isotactic index greater than 80, or a copolymer selected from the group
consisting of a copolymer of (a) propylene and ethylene, (b) propylene,
ethylene and a 4-8 C alpha-olefin, and (c) propylene and a 4-8 C
alpha-olefin, the copolymer having a polymerized propylene content of more
than 85% by weight and an isotactic index greater than 85;
(ii) about 5% to about 25% of a copolymer of ethylene and propylene or a
4-8 C alpha-olefin that is insoluble in xylene at ambient temperature, and
(iii) about 30% to about 70% of an elastomeric copolymer selected from the
group consisting of a copolymer of (a) ethylene and propylene, (b)
ethylene, propylene, and a 4-8 C alpha-olefin, and (c) ethylene and a 4-8
C alpha-olefin, the copolymer optionally containing about 0.5% to about
10% of a polymerized diene, and containing less than 70% by weight of
polymerized ethylene and being soluble in xylene at ambient temperature,
and having an intrinsic viscosity of about 1.5 to about 4.0 dl/g,
wherein the total amount of (ii) and (iii), based on the total olefin
polymer composition, is about 50% to about 90%, the weight ratio of
(ii)/(iii) is less than 0.4, and the composition is prepared by
polymerization in at least two stages, and has a flexural modulus of less
than 150 MPa; or
(e) a thermoplastic olefin comprising:
(i) about 10% to about 60% of a propylene homopolymer having an isotactic
index greater than 80, or a copolymer selected from the group consisting
of a copolymer of (a) ethylene and propylene, (b) ethylene, propylene, and
a 4-8 C alpha-olefin, and (c) ethylene and a 4-8 C alpha-olefin, the
copolymer having a polymerized propylene content greater than 85% and an
isotactic index of greater than 85;
(ii) about 20% to about 60% of an amorphous copolymer selected from the
group consisting of a copolymer of (a) ethylene and propylene, (b)
ethylene, propylene, and a 4-8 C alpha-olefin, and (c) ethylene and a 4-8
C alpha-olefin, the copolymer optionally containing about 0.5% to about
10% of a polymerized diene and containing less than 70% polymerized
ethylene and being soluble in xylene at ambient temperature; and
(iii) about 3% to about 40% of a copolymer of ethylene and propylene or a
4-8 C alpha-olefin that is insoluble in xylene at ambient temperature,
wherein the thermoplastic olefin has a flexural modulus of greater than
150 but less than 1200 MPa.
10. The method of claim 9 wherein the propylene polymer material is a
propylene homopolymer.
11. The method of claim 8 wherein an ester of an acrylic acid substituted
at the .alpha.-carbon atom by a 1-3 C alkyl group is polymerized.
12. The method of claim 11 wherein the ester is methyl methacrylate.
13. The method of claim 8 wherein the 4vinyl-substituted cyclic 1-alkene is
4-vinyl-1-cyclohexene.
14. The method of claim 12 wherein the 4-vinyl-substituted cyclic 1-alkene
is 4-vinyl-1-cyclohexene.
Description
FIELD OF THE INVENTION
This invention relates to a process for making thermally stable polymers of
polymerizable acrylic monomers and grafted polymers of a propylene polymer
material and a polymerizable acrylic monomer.
BACKGROUND OF THE INVENTION
Alpha-substituted polymers such as polymerized methacrylates,
methacrylonitriles, and alpha-methylstyrene are thermally unstable and are
known to depolymerize to their corresponding monomers at temperatures
greater than .about.180.degree. C., depending upon the molecular weight of
the polymer. Above 300.degree. C., poly(methyl methacrylate)(PMMA)
depolymerizes rapidly at high conversions (about 95% or more). Typical
extruding and molding temperatures for such polymers are
200.degree.-290.degree. C. Significant depolymerization to the respective
monomers would occur in this temperature range, affecting the safety of
the operation as well as the properties of the resulting product.
Polymethacrylates, and in particular PMMA, are the alpha-substituted
polymers most widely used in commercial applications. In order to broaden
the range of applications for these polymers it is critical to improve
their thermal oxidative stability.
In the manufacture of grafted polymers comprising a backbone of a propylene
polymer material, to which is grafted PMMA, small amounts of monomers such
as methyl acrylate, butyl acrylate and styrene are typically copolymerized
with the methyl methacrylate to improve thermal stability, since polymers
of these monomers are much more stable to heat and undergo degradation at
relatively higher temperatures. However, addition of these monomers
affects the mechanical properties of the resulting grafted polymers as
well as the molecular weight of the polymers and the efficiency of the
graft polymerization reaction.
There is still a need for a method to increase the thermal oxidative
stability of grafted polymers that include polymerized acrylic monomers,
compared with that achievable with the comonomers currently used for this
purpose.
SUMMARY OF THE INVENTION
The graft copolymer of this invention comprises a backbone of a propylene
polymer material to which is graft polymerized chains of (i) an ester or
salt of an unsubstituted or 1-3 C alkyl-substituted acrylic acid or (ii)
an ester or salt of an unsubstituted or 1-3 C alkyl-substituted acrylic
acid and about 1 to about 10 mole %, based on the total monomers added, of
an unsubstituted or 1-3 C alkyl-substituted acrylic acid, having
4-ethylidene-substituted 5-12 C cyclic 1-alkene groups at the chain ends.
Another embodiment of this invention comprises a polymer of monomers
selected from the group consisting of (i) an ester or salt of an
unsubstituted or 1-3 C alkyl-substituted acrylic acid and (ii) an ester or
salt of an unsubstituted or 1-3 C alkyl-substituted acrylic acid and about
1 to about 10 mole %, based on the total monomers added, of an
unsubstituted or 1-3 C alkyl-substituted acrylic acid, having end groups
comprising 4-ethylidene-substituted 5-12 C cyclic 1-alkene groups.
In another embodiment, the method of this invention for improving the
thermal oxidative stability of acrylic grafted polymers comprises:
(a) graft polymerizing monomers selected from the group consisting of (i)
an ester or salt of an unsubstituted or 1-3 C alkyl-substituted acrylic
acid and (ii) an ester or salt of an unsubstituted or 1-3 C
alkyl-substituted acrylic acid and about 1 to about 10 mole %, based on
the total monomers added, of an unsubstituted or 1-3 C alkyl-substituted
acrylic acid, to a backbone of a propylene polymer material in the
presence of a 4vinyl-substituted 5-12 C cyclic 1-alkene, wherein the total
amount of polymerized monomer is about 20 to about 200 parts per hundred
parts of the propylene polymer material and the 4-vinyl-substituted cyclic
1-alkene is present in an amount of about 1 mole % to about 30 mole %,
based on the total moles of monomers added, and
(b) removing any unreacted grafting monomer from the resulting grafted
propylene polymer material, decomposing any unreacted initiator, and
deactivating any residual free radicals in the material,
wherein steps (a) and (b) are carried out in a substantially non-oxidizing
environment.
The 4-ethylidene-substituted cyclic 1-alkene groups attach at the ends of
the chains of polymerized acrylic monomer and significantly increase the
thermal oxidative stability of grafted as well as ungrafted polymer. The
room temperature mechanical properties and molecular weight of the grafted
polymer, and the grafting efficiency of the process are not adversely
affected.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of temperature (.degree.C.) against the % of the original
weight of the grafted polymer and shows the weight loss during
thermogravimetric analysis (TGA) in air and therefore the thermal
oxidative stability of the grafted polymers. The grafted polymers comprise
a backbone of propylene homopolymer, to which was grafted poly(methyl
methacrylate) having 4-ethylidenecyclohex-1-ene (VCH) groups at the chain
ends (PMMA/VCH), polypropylene grafted with poly(methyl
methacrylate-co-methyl acrylate) (PMMA-co-MeAc), and polypropylene grafted
with poly(methyl methacrylate-co-styrene) (PMMA-co-St). The number average
molecular weight (M.sub.n) of the free poly(methyl methacrylate) (PMMA)
was 75,000-90,000.
FIG. 2 is a plot of temperature (.degree.C.) against the % of the original
weight of the polymer and shows the weight loss during TGA in air and
therefore the thermal oxidative stability of the polymers. The polymers
comprise poly(methyl methacrylate) having 4-ethylidenecyclohex-1-ene
groups at the chain ends and containing various amounts of
4-ethylidenecyclohex-1-ene groups, poly(methyl methacrylate), and
poly(methyl methacrylate-co-methyl acrylate) containing various amounts of
polymerized methyl acrylate. The M.sub.n of the PMMA was 4600-5100.
FIG. 3 is a plot of temperature (.degree.C.) against the weight loss of
polymers of much lower molecular weight and shows the % weight loss during
TGA in air and therefore the thermal oxidative stability of the polymers.
The polymers comprise poly(methyl methacrylate) having
4-ethylidenecyclohex-1-ene groups at the chain ends and containing various
amounts of 4-ethylidenecyclohex-1-ene groups (4, 5), poly(methyl
methacrylate) (1), and poly(methyl methacrylate-co-methyl acrylate)
containing various amounts of polymerized methyl acrylate (2, 3). The
M.sub.n of the PMMA was 981-1399.
DETAILED DESCRIPTION OF THE INVENTION
The first step in the process of this invention for improving the thermal
oxidative stability of acrylic grafted polymers is graft polymerizing
monomers selected from the group consisting of (i) an ester or salt of an
unsubstituted or 1-3 C alkyl-substituted acrylic acid and (ii) an ester or
salt of an unsubstituted or 1-3 C alkyl-substituted acrylic acid and about
1 to about 10 mole %, based on the total monomers added, of an
unsubstituted or 1-3 C alkyl-substituted acrylic acid, in a substantially
non-oxidizing environment, to a backbone of a propylene polymer material
in the presence of a 4-vinyl-substituted 5-12 C cyclic 1-alkene. The graft
copolymers have 4-ethylidene-substituted 5-12 C cyclic 1-alkene groups at
the ends of the chains of polymerized acrylic monomers.
The propylene polymer material that is used as the backbone of the graft
copolymer can be:
(a) a homopolymer of propylene having an isotactic index greater than 80,
preferably about 85 to about 99;
(b) a copolymer of propylene and an olefin selected from the group
consisting of ethylene and 4-10 C alpha-olefins, provided that when the
olefin is ethylene, the maximum polymerized ethylene content is 10% by
weight, preferably about 4%, and when the olefin is a 4-10 C alpha-olefin,
the maximum polymerized content thereof is 20% by weight, preferably about
16%, the copolymer having an isotactic index greater than 85;
(c) a terpolymer of propylene and two olefins selected from the group
consisting of ethylene and 4-8 C alpha-olefins, provided that the maximum
polymerized 4-8 C alpha-olefin content is 20% by weight, preferably about
16%, and, when ethylene is one of the olefins, the maximum polymerized
ethylene content is 5% by weight, preferably about 4%, the terpolymer
having an isotactic index greater than 85;
(d) an olefin polymer composition comprising:
(i) about 10% to about 60% by weight, preferably about 15% to about 55%, of
a propylene homopolymer having an isotactic index greater than 80,
preferably about 85 to about 98, or a copolymer selected from the group
consisting of a copolymer of (a) propylene and ethylene, (b) propylene,
ethylene and a 4-8 C alpha-olefin, and (c) propylene and a 4-8 C
alpha-olefin, the copolymer having a polymerized propylene content of more
than 85% by weight, preferably about 90% to about 99%, and an isotactic
index greater than 85;
(ii) about 5% to about 25%, preferably about 5% to about 20%, of a
copolymer of ethylene and propylene or a 4-8 C alpha-olefin that is
insoluble in xylene at ambient temperature, and
(iii) about 30% to about 70%, preferably about 40% to about 65%, of an
elastomeric copolymer selected from the group consisting of a copolymer of
(a) ethylene and propylene, (b) ethylene, propylene, and a 4-8 C
alpha-olefin, and (c) ethylene and a 4-8 C alpha-olefin, the copolymer
optionally containing about 0.5% to about 10% of a polymerized diene, and
containing less than 70% by weight, preferably about 10% to about 60%,
most preferably about 12% to about 55%, of polymerized ethylene and being
soluble in xylene at ambient temperature, and having an intrinsic
viscosity of about 1.5 to about 4.0 dl/g,
wherein the total amount of (ii) and (iii), based on the total olefin
polymer composition, is about 50% to about 90%, the weight ratio of
(ii)/(iii) is less than 0.4, preferably 0.1 to 0.3, and the composition is
prepared by polymerization in at least two stages, and has a flexural
modulus of less than 150 MPa; or
(e) a thermoplastic olefin comprising:
(i) about 10% to about 60%, preferably about 20% to about 50%, of a
propylene homopolymer having an isotactic index greater than 80, or a
copolymer selected from the group consisting of a copolymer of (a)
ethylene and propylene, (b) ethylene, propylene, and a 4-8 C alpha-olefin,
and (c) ethylene and a 4-8 C alpha-olefin, the copolymer having a
polymerized propylene content greater than 85% and an isotactic index of
greater than 85;
(ii) about 20% to about 60%, preferably about 30% to about 50%, of an
amorphous copolymer selected from the group consisting of a copolymer of
(a) ethylene and propylene, (b) ethylene, propylene, and a 4-8 C
alpha-olefin, and (c) ethylene and a 4-8 C alpha-olefin, the copolymer
optionally containing about 0.5% to about 10% of a polymerized diene and
containing less than 70% polymerized ethylene and being soluble in xylene
at ambient temperature; and
(iii) about 3% to about 40%, preferably about 10% to about 20%, of a
copolymer of ethylene and propylene or a 4-8 C alpha-olefin that is
insoluble in xylene at ambient temperature, wherein the thermoplastic
olefin has a flexural modulus of greater than 150 but less than 1200 MPa,
preferably about 200 to about 1100 MPa, most preferably about 200 to about
1000 MPa.
Room or ambient temperature is about 25.degree. C.
4-8 C Alpha-olefins useful in the preparation of (d) and (e) include, for
example, butene-1; pentene-1; hexene-1; 4-methylpentene-1, and octene-1.
The diene, when present, is typically a butadiene; 1,4-hexadiene;
1,5-hexadiene, or ethylidenenorbornene.
Propylene polymer materials (d) and (e) can be prepared by polymerization
in at least two stages, where in the first stage the propylene; propylene
and ethylene; propylene and an alpha-olefin, or propylene, ethylene and an
alpha-olefin are polymerized to form component (i) of (d) or (e), and in
the following stages the mixtures of ethylene and propylene; ethylene and
the alpha-olefin, or ethylene, propylene and the alpha-olefin, and
optionally a diene, are polymerized to form components (ii) and (iii) of
(d) or (e).
The polymerization can be conducted in liquid phase, gas phase, or
liquid-gas phase using separate reactors, all of which can be done either
by batch or continuously. For example, it is possible to carry out the
polymerization of component (i) using liquid propylene as a diluent, and
the polymerization of components (ii) and (iii) in gas phase, without
intermediate stages except for the partial degassing of the propylene. All
gas phase is the preferred method.
The preparation of propylene polymer material (d) is described in more
detail in U.S. Pat. Nos. 5,212,246 and 5,409,992, which patents are
incorporated herein by reference. The preparation of propylene polymer
material (e) is described in more detail in U.S. Pat. Nos. 5,302,454 and
5,409,992, which patents are incorporated herein by reference.
Propylene homopolymer is the preferred propylene polymer backbone material.
The monomers that are graft polymerized onto the backbone of propylene
polymer material are selected from the group consisting of (i) an ester or
salt of an unsubstituted or 1-3 carbon (C) alkyl-substituted acrylic acid
and (ii) an ester or salt of an unsubstituted or 1-3 C alkyl-substituted
acrylic acid and about 1 to about 10 mole %, based on the total monomers
added, of an unsubstituted or 1-3 C alkyl-substituted acrylic acid.
Methacrylic acid is the preferred substituted acrylic acid. Suitable
esters include, for example, the methyl, ethyl, butyl, benzyl,
phenylethyl, phenoxyethyl, epoxypropyl, and hydroxypropyl esters. Esters
of 1-4 C alkanols are preferred. Methyl methacrylate is most preferred.
Suitable salts include, for example, the sodium, calcium, or magnesium
salts.
The graft polymerization of the acrylic monomer is carried out in the
presence of a 4-vinyl-substituted 5-12 C cyclic 1-alkene, preferably
4vinyl-1-cyclohexene. The 4-vinyl-substituted cyclic 1-alkene is present
in an amount of about 1 mole % to about 30 mole %, preferably about 2 to
about 16 mole %, based on the total moles of monomers added. Nuclear
magnetic resonance studies have shown that the 4-vinyl-substituted cyclic
1-alkene does not polymerize or copolymerize by a free radical mechanism
and groups derived from 4-vinyl-substituted cyclic 1-alkenes by
rearrangement of the double bonds are present only at the ends of the
chains of polymerized acrylic monomer. For example, when
4-vinyl-1-cyclohexene reacts at the ends of the chains of polymerized
acrylic monomer, 4-ethylidenecyclohex-1-ene groups are formed.
It is known that low molecular weight polymers are less stable than those
with high molecular weight. The 4vinyl-substituted cyclic 1-alkenes of
this invention are effective in thermal oxidative stabilization of both
grafted and ungrafted acrylic polymers in which the M.sub.n of the
polymerized acrylic monomer is as low as 1000 and the polydispersity
(M.sub.w /M.sub.n) is about 3.
The total amount of polymerized monomers is about 20 to about 200 parts,
preferably about 20 to about 100 parts, per hundred parts of the propylene
polymer material.
The grafted polymer can be made according to any one of various methods.
One of these methods involves forming active grafting sites on the
propylene polymer material by treatment with a peroxide or other chemical
compound that is a free radical polymerization initiator, or by
irradiation with high energy ionizing radiation. The free radicals
produced in the polymer as a result of the chemical or irradiation
treatment form active grafting sites on the polymer and initiate the
polymerization of the monomers at these sites. Grafted polymers produced
by peroxide-initiated grafting methods are preferred.
During the graft polymerization, the monomers also polymerize to form a
certain amount of free or ungrafted polymer or copolymer. The morphology
of the grafted polymer is such that the propylene polymer material is the
continuous or matrix phase, and the polymerized monomers, both grafted and
ungrafted, are a dispersed phase. The reaction of the 4-vinyl-substituted
cyclic 1-alkenes at the ends of the chains of the polymerized acrylic
monomers increases the thermal oxidative stability of both the grafted and
ungrafted polymerized monomers.
The last step of the process of this invention is removing any unreacted
grafting monomer from the resulting grafted propylene polymer material,
decomposing any unreacted initiator, and deactivating any residual free
radicals in the material. This step is carried out in a substantially
non-oxidizing environment.
The expression "substantially non-oxidizing environment" means an
environment in which the active oxygen concentration, i.e., the
concentration of oxygen in a form that will react with the free radicals
in the polymer material, is less than about 15%, preferably less than
about 5%, and most preferably less than about 1%, by volume. The most
preferred concentration of active oxygen is 0.004% or lower by volume.
Within these limits, the non-oxidizing atmosphere can be any gas, or
mixture of gases, which is oxidatively inert toward the free radicals in
the propylene polymer material, e.g., nitrogen, argon, helium and carbon
dioxide.
Preparation of grafted polymers by contacting the propylene polymer with a
free radical polymerization initiator such as an organic peroxide and a
vinyl monomer is described in more detail in U.S. Pat. No. 5,140,074,
which is incorporated herein by reference.
Preparation of grafted polymers by irradiating an olefin polymer and then
treating with a vinyl monomer is described in more detail in U.S. Pat. No.
5,411,994, which is incorporated herein by reference.
Compositions containing the grafted polymers of this invention can easily
be impact-modified by the addition of one or more rubber components
selected from the group consisting of (i) an olefin copolymer rubber, (ii)
a monoalkenyl aromatic hydrocarbon-conjugated diene block copolymer, and
(iii) a core-shell rubber. Any of these rubber components can have acid or
anhydride functionality or can be free of these functional groups. The
preferred rubber components are (i) and (ii), either alone or in
combination.
Suitable olefin copolymer rubbers include, for example, saturated olefin
copolymer rubbers such as ethylene/propylene monomer rubbers (EPM),
ethylene/octene-1, and ethylene/butene-1 rubbers, and unsaturated olefin
terpolymer rubbers such as ethylene/propylene/diene monomer rubbers
(EPDM). The preferred olefin copolymer rubbers are ethylene/propylene,
ethylene/butene-1, and ethylene/octene-1 copolymer rubbers.
The monoalkenyl aromatic hydrocarbon-conjugated diene block copolymer can
be a thermoplastic elastomer of the A-B (or diblock) structure, the linear
A-B-A (or triblock) structure, the radial (A-B).sub.n type where n=3-20%,
or a combination of these structure types, wherein each A block is a
monoalkenyl aromatic hydrocarbon polymer block, and each B block is an
unsaturated rubber block. Various grades of copolymers of this type are
commercially available. The grades differ in structure, molecular weight
of the mid and end blocks, and ratio of monoalkenyl aromatic hydrocarbon
to rubber. The block copolymer can also be hydrogenated Typical
monoalkenyl aromatic hydrocarbon monomers are styrene, ring-substituted
1-4 C linear or branched alkyl styrenes, and vinyltoluene. Styrene is
preferred. Suitable conjugated dienes include, for example, butadiene and
isoprene. Preferred block copolymers are hydrogenated
styrene/ethylene-butene/styrene triblock copolymers.
The weight average molecular weight (M.sub.w) of the block copolymers
generally will be in the range of about 45,000 to about 260,000 g/mole,
average molecular weights in the range of about 50,000 to about 125,000
g/mole being preferred because they produce compositions having the best
balance of impact strength and stiffness. Also, while block copolymers
having unsaturated as well as saturated rubber blocks can be used,
copolymers having saturated rubber blocks are preferred, also on the basis
of the impact/stiffness balance of the compositions containing them. The
weight ratio of monoalkenyl aromatic hydrocarbon to conjugated diene
rubber in the block copolymer is in the range of about 5/95 to about
50/50, preferably about 10/90 to about 40/60.
The core-shell rubber components comprise small particles of crosslinked
rubber phase surrounded by a compatibilizing shell, normally a glassy
polymer or copolymer. The core is typically a diene rubber such as
butadiene or isoprene, or an acrylate. The shell is typically a polymer of
two or more monomers selected from styrene, methyl methacrylate, and
acrylonitrile. Particularly preferred core-shell rubbers have an acrylate
core.
Suitable impact modifiers include, for example, Engage 8100, 8150, and 8200
ethylene/octene-1 copolymers, commercially available from DuPont Dow
Elastomers; EPM 306P random ethylene/propylene copolymer, commercially
available from Miles Inc., Polysar Rubber Division; Kraton G 1652
styrene/ethylene-butene/styrene triblock copolymer, commercially available
from Shell Chemical Company; Exact ethylene/butene-1 copolymers,
commercially available from Exxon Chemical Company, and KS080 and KS350
heterophasic polyolefins, commercially available from Montell USA Inc.
The impact modifier, if present, is used in an amount of about 2% to about
30%, preferably about 5% to about 15%, by weight, based on the total
weight of the composition.
The composition can also contain a broad molecular weight distribution
(M.sub.w /M.sub.n) propylene polymer material (BMWD PP). The BMWD PP has a
M.sub.w /M.sub.n of about 5 to about 60, preferably about 5 to about 40; a
melt flow rate of about 0.5 to about 50, preferably about 1 to about 30,
g/10 min, and xylene insolubles at 25.degree. C. of greater than or equal
to 94%, preferably greater than or equal to 96%, and most preferably
greater than or equal to 98%. The propylene polymer material having a
broad molecular weight distribution can be a homopolymer of propylene or
an ethylene/propylene rubber impact-modified homopolymer of propylene,
wherein the propylene homopolymer has a broad molecular weight
distribution.
The BMWD PP can be prepared by sequential polymerization in at least two
stages, in the presence of a Ziegler-Natta catalyst supported on magnesium
halide in active form. The polymerization process occurs in separate and
consecutive stages, and in each stage polymerization takes place in the
presence of the polymer and the catalyst coming from the preceding stage.
The polymerization process can be carried out in a batch or in a continuous
mode according to known techniques, operating in liquid phase in the
presence or not of an inert diluent, or in gas phase, or liquid-gas phase,
preferably in gas phase. The preparation of the BMWD PP is described in
more detail in U.S. Pat. No. 5,286,791, which patent is incorporated
herein by reference.
The BMWD PP, if present, is used in an amount of about 5% to about 90%,
preferably about 10% to about 70%, based on the total weight of the
composition.
Other additives such as fillers and reinforcing agents, e.g., carbon black
and glass fibers, as well as inorganic powders such as calcium carbonate,
talc, and mica; pigments; slip agents; waxes; oils; antiblocking agents,
and antioxidants can also be present.
Polymers of monomers selected from the group consisting of (i) an ester or
salt of an unsubstituted or 1-3 C alkyl-substituted acrylic acid and (ii)
an ester or salt of an unsubstituted or 1-3 C alkyl-substituted acrylic
acid and about 1 to about 10 mole %, based on the total monomers added, of
an unsubstituted or 1-3 C alkyl-substituted acrylic acid, having end
groups comprising 4-ethylidene-substituted 5-12 C cyclic 1-alkene groups
can be prepared by polymerizing the monomer in a hydrocarbon solvent in
the presence of about 1 mole % to about 30 mole %, preferably about 2 mole
% to about 16 mole %, based on the total moles of monomer added, of a
4-vinyl-substituted 5-12 C cyclic 1-alkene. A free radical polymerization
initiator such as an organic peroxide is used. The polymerization can also
be carried out in water emulsion in the presence of a suitable emulsifier
and a water-soluble free radical initiator.
The test methods used to evaluate the molded specimens were:
Flexural modulus ASTM D-790-86
Tensile strength ASTM D-638-89
Elongation @ yield ASTM D-638-89
Melt flow rate, 230.degree. C., 3.8 kg ASTM 1238
The porosity of the propylene homopolymer used as the backbone polymer in
the manufacture of graft copolymers is measured as described in Winslow,
N. M. and Shapiro, J. J., "An Instrument for the Measurement of Pore-Size
Distribution by Mercury Penetration," ASTM Bull., TP 49, 3944 (February
1959), and Rootare, H. M., "Review of Mercury Porosimetry," 225-252 (In
Hirshhom, J. S. and Roll, K. H., Eds., Advanced Experimental Techniques in
Powder Metallurgy, Plenum Press, New York 1970).
Isotactic index is defined as the xylene insoluble fraction. The weight
percent of olefin polymer soluble in xylene at room temperature is
determined by dissolving 2.5 g of the polymer in 250 ml of xylene in a
vessel equipped with a stirrer that is heated at 135.degree. C. with
agitation for 20 minutes. The solution is cooled to 25.degree. C. while
continuing the agitation, and then left to stand without agitation for 30
minutes so that the solids can settle. The solids are filtered with filter
paper, the remaining solution is evaporated by treating it with a nitrogen
stream, and the solid residue is vacuum dried at 80.degree. C. until a
constant weight is reached. The percent by weight of polymer insoluble in
xylene at room temperature is the isotactic index of the polymer. The
value obtained in this manner corresponds substantially to the isotactic
index determined via extraction with boiling n-heptane, which by
definition constitutes the isotactic index of the polymer.
Intrinsic viscosity was measured in tetrahydronaphthalene at 135.degree. C.
Molecular weight measurements were made by gel permeation chromatography.
In this specification, all parts and percentages are by weight unless
otherwise noted.
EXAMPLE 1
This example demonstrates the thermal oxidative stability of a grafted
polymer comprising a propylene homopolymer backbone, to which was graft
polymerized poly(methyl methacrylate) having 4-ethylidenecyclohex-1-ene
groups at the ends of the polymerized methyl methacrylate chains
(PP-g-PMMA/VCH), compared with polypropylene to which was grafted
polymerized a methyl methacrylate/styrene copolymer (PP-g-PMMA-co-St) or a
methyl methacrylate/methyl acrylate copolymer (PP-g-PMMA-co-MeAc).
In this and the following examples the propylene homopolymer used as the
backbone polymer had the following properties: spherical form, melt flow
rate (MFR) of 9 g/10 min, a porosity of 0.45 cm.sup.3 /g and a weight
average molecular weight (M.sub.w) of 170,000.
The PP-g-PMMA VCH grafted polymer was prepared as follows. The MMA was
graft polymerized onto the polypropylene backbone at a temperature of
92.degree. C. using the previously described peroxide-initiated graft
polymerization process, in the presence of 10 mole %
4-vinyl-1-cyclohexene. Forty-five parts by weight of monomer were added
per 100 parts of polypropylene. Tert-butylperoxy pivalate (75 wt. %
solution in odorless mineral spirits) was used as the peroxide initiator.
The monomers were fed at a rate of .about.1.1 pph/min for 42 minutes. A
monomer to initiator molar ratio of 91 was used. After the addition of
monomers the mixture was stirred at the same temperature for another 2.5
hours under a nitrogen purge. The conversion of monomer to polymer was
79%.
The PP-g-PMMA-o-MeAc graft copolymer was prepared as follows. The monomers
were grafted onto the polypropylene backbone at a grafting temperature of
92.degree.-95.degree. C. 48.8 Parts by weight of monomers were added per
100 parts of polypropylene. Tert-butylperoxy pivalate was used as the
initiator at a monomer to initiator molar ratio of 100. The monomers were
fed at a rate of 1.4 pph/min over a period of 35 minutes. After the
addition of the monomers the mixture was stirred at the same temperature
for another 2.5 hours under a nitrogen purge. The conversion of monomers
to polymer was 93%.
The PP-g-PMMA-co-St graft copolymer was prepared as follows. Fifty parts by
weight of monomers were added per 100 parts of polypropylene at a reaction
temperature of 92.degree. C. Tert-butylperoxy pivalate was used as the
initiator at a monomer to initiator molar ratio of 100. The monomers were
fed at a rate of 1.24 pph/min over a period of 30 minutes. After the
addition of the monomers the mixture was stirred at the same temperature
for another 2.5 hours under a nitrogen purge. The conversion of monomers
to polymer was 94%.
The graft copolymers were stabilized with 0.14% Irganox B215, a mixture of
1 part Irganox 1010
tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]-methane
stabilizer and 2 parts Irgafos 168 tris(2,4-di-tert-butylphenyl) phosphite
stabilizer, commercially available from Ciba Specialty Chemicals Company,
and 0.06% calcium stearate.
The thermal oxidative stability of the pelletized samples was assessed by
thermogravimetric analysis (TGA) using a Perkin-Elmer TGA-7 analyzer.
About 15 mg of sample were scanned at 10.degree. C./min in air from
25.degree. C. to 900.degree. C. and the weight loss was monitored. The
region of interest lies between 200.degree. C. and 350.degree. C., where
poly(methyl methacrylate) tends to lose weight by depolymerization. The
results are shown in FIG. 1. The weight average molecular weight (M.sub.w)
and number average molecular weight (M.sub.n) of the free PMMA in the
polymers are given in Table 1.
The data show that the grafted polymer having 4-ethylidenecyclohex-1-ene
groups at the ends of the polymerized methyl methacrylate chains was more
stable at a given temperature than the PP-g-PMMA-co-MeAc or PP-g-PMMA--St
graft copolymers.
EXAMPLE 2
This example demonstrates the physical properties of a graft copolymer
comprising a propylene homopolymer backbone, to which was graft
polymerized poly(methyl methacrylate) having 4-ethylidenecyclohex-1-ene
groups at the ends of the PMMA chains, compared with polypropylene grafted
with poly(methyl methacrylate-co-methyl acrylate) or poly(methyl
methacrylate-co-styrene).
The graft copolymers were prepared as described in Example 1 and the same
stabilizers in the same amounts as in Example 1 were used.
The samples were dried at 80.degree. C. for at least 4 hours prior to
molding to remove surface moisture. One inch.times.1/8 inch test bars were
used for all of the physical property measurements. The samples were
extruded on a Haake mixer and test bars were produced on a 5 oz Battenfeld
injection molding machine at a barrel temperature of 465.degree. F. and a
mold temperature of 145.degree. F. The results of the property evaluations
for each sample as well as the M.sub.n and M.sub.w of the free poly(methyl
methacrylate) (PMMA) are given in Table 1.
TABLE 1
PP-g- PP-g-
PMMA- PMMA- PP-g-
Graft Copolymer co-St co-MeAc PMMA/VCH
M.sub.w PMMA 525000 453000 522000
M.sub.n PMMA 89000 75000 90000
MFR (g/10 min) 4.2 3.2 4.9
Flex Mod 1% Sec (kpsi) 247 256 242
Tensile Strength @ yield (kpsi) 5.3 5.4 5.3
Elongation @ Yield (1%) 4.9 4.8 5.6
The data show that the graft copolymer containing
4-ethylidenecyclohex-1-ene groups at the end of the PMMA chains exhibited
properties similar to those of the PP-g-(PMMA-co-MeAc) or
PP-g-(PMMA-co-St) graft copolymers.
EXAMPLE 3
This example demonstrates the thermal oxidative stability of a polymer
comprising poly(methyl methacrylate) having 4-ethylidenecyclohex-1-ene
groups at the ends of the PMMA chains and containing various amounts of
4-hylidenecyclohex-1-ene groups, compared with poly(methyl methacrylate)
and poly(methyl methacrylate-co methyl acrylate) containing various
amounts of polymerized methyl acrylate.
The PMMA was prepared as follows. The monomer was polymerized in toluene at
a temperature of 85.degree. C. over a period of 3 hours. Tert-butylperoxy
pivalate was used as the peroxide initiator at a monomer to initiator
molar ratio of 40. The conversion of monomer to polymer was 70%.
The PMMA-co-MeAc copolymers were prepared as described above except that
4.8 and 9.1 mole % respectively of MeAc were added to the MMA.
The PP-g-PMMA/VCH polymers were prepared as described above except that
2.2, 4.4 and 8.4 mole % respectively of VCH were added to the MMA These
polymers were not stabilized.
The thermal oxidative stability of the polymers was assessed as described
in Example 1. The results are shown in FIG. 2. The M.sub.n of the PMMA is
given for each sample.
The data show that the polymers having 4-ethylidenecyclohex-1-ene groups at
the ends of the chains of PMMA and containing various amounts of
4-ethylidenecyclohex-1-ene groups were more stable at a given temperature
than PMMA or poly(methyl methacrylate-co-methyl acrylate) containing
various amounts of polymerized methyl acrylate. A determination that the
oxidative thermal stability of the PMMA increases when
4-ethylidenecyclohex-1-ene groups are present at the chain ends, is an
indication that chains of graft polymerized PMMA with
4-ethylidenecyclohex-1-ene groups at the chain ends will also be more
stable.
EXAMPLE 4
This example demonstrates the thermal oxidative stability of low molecular
weight poly(methyl methacrylate) having 4-ethylidenecyclohex-1-ene groups
at the ends of the PMMA chains and containing various amounts of
4-ethylidenecyclohex-1-ene groups, compared with poly(methyl methacrylate)
and poly(methyl methacrylate-co-methyl acrylate) containing various
amounts of polymerized methyl acrylate.
The PMMA was prepared as follows. The monomer was polymerized at a
temperature of 90.degree. C. in toluene over a period of 2 hours.
Tert-butylperoxy pivalate was used as the peroxide initiator at a monomer
to initiator molar ratio of 13.5. The % conversion of monomer to polymer
is given in Table 2.
The poly(MMA-co-MeAc) copolymers were prepared as described above except
that 8.4 and 16.5 mole % respectively of MeAc were added to the MMA.
The PMMA/VCH polymers were prepared as described above except that 7.7 and
15.3 mole % respectively of VCH were added to the MMA.
These polymers were not stabilized for the thermal study.
The thermal oxidative stability of the samples were assessed as described
in Example 1. The results are shown in FIG. 3. Sample 1 was PMMA, Sample 2
was poly MA-co-MeAc) (8.4 mole % MeAc), Sample 3 was poly(MMA-co-MeAc)
(16.5 mole % MeAc), Sample 4 was PMMA/VCH) (7.7 mole % VCH) and Sample 5
was PMMA/VCH (15.3 mole % VCH).
The M.sub.w and M.sub.n of the PMMA, and % weight loss at 2000 and
250.degree. C. for each sample are given in Table 2.
TABLE 2
Sample 1 2 3 4 5
MeAc (mol %) 0 8.4 16.5 0 0
VCH (mol %) 0 0 0 7.7 15.3
Conversion (%) 60 65 60 70 65
M.sub.w PMMA 4009 4156 4867 3078 3405
M.sub.n PMMA 1399 1392 1278 1224 981
Thermal Stability
Wt. Loss (%) (200.degree. C.) 5.7 3.5 3.2 1.6 1.3
Wt. Loss (%) (250.degree. C.) 14.1 9.7 8.9 6.8 5.8
The data show that the polymers containing various amounts of
4-ethylidenecyclohex-1-ene groups at the ends of the PMMA chains were more
stable at a given temperature than the PMMA or poly(methyl
methacrylate-co-methyl acrylate) containing various amounts of polymerized
methyl acrylate. A determination that the thermal oxidative stability of
the PMMA increases when 4-ethylidenecyclohex-1-ene groups are present at
the chain ends, is an indication that chains of graft polymerized PMMA
with 4-ethylidenecyclohex-1-ene groups at the chain ends will also be more
stable.
Other features, advantages and embodiments of the invention disclosed
herein will be readily apparent to those exercising ordinary skill after
reading the foregoing disclosures. In this regard, while specific
embodiments of the invention have been described in considerable detail,
variations and modifications of these embodiments can be effected without
departing from the spirit and scope of the invention as described and
claimed.
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